1. Field of Invention
The field of the present invention relates in general to optical networks and more particularly to optical receivers.
2. Description of the Related Art
In communication systems light beams are increasingly used for transmitting information. The demand for communication bandwidth has resulted in a conversion of long and short haul communication trunk lines from copper to fiber optic (digital) communication. The wide spectral characteristics of fiber optics support broadband signals at very high data rates, gigabits per second.
Generally, an optical source, i.e. transmitter, converts an electrical signal, either digital or analog, to a modulated light beam which is then passed through an optical fiber to an optical detector, i.e. receiver, that extracts an electrical signal from the received light beam. A fiber may be shared with different communication channels using frequency, time or other forms of multiplexing. A typical optical link extends the range of a communication system with a transceiver unit that handles opto-electronic conversion between an optical fiber(s) and local area networks (LAN) on opposing ends of the fiber. Optical transceivers offer gigabit communication rates over long haul trans-oceanic cables or short range links in a metropolitan area.
A typical transmitter operates at a fixed power level. An optical link may range in distance from several meters to a hundred kilometers thereby delivering a broad range of optical signal levels at the optical receiver. The optical receiver must function with both precision and accuracy over the broad range of received optical signal levels. Typically an optical receiver includes either a positive-intrinsic-negative (PIN) type or an avalanche photo-diode (APD) type photo-detector. The two types have different gain and signal-to-noise characteristics both of which vary with operational parameters such as the bias voltage and temperature. Both types of photodetectors require monitoring of parameters such as received optical power and temperature to assure the received signal is in appropriate range to ensure proper decoding of data at receiver. Typically regulation of gain and signal-to-noise characteristics is approached with analog circuitry and monitoring with digital circuitry.
What is needed are new means for regulation and monitoring of photo-detectors which avoid the complexity and expense of prior art approaches.